Dissolved Organic Matter in Delaware Waters Dissolved organic matter (DOM) is a dominant carbon source for heterotrophs contributing to water quality issues in estuarine systems and represents an important input of reduced carbon to the ocean. It is important to understand how the sources of DOM influence its composition and impacts in coastal waterways. As part of the multi-institutional, multi-investigator, collaborative Project WiCCED (Water in the Changing Coastal Climate of Delaware) funded by NSF EPSCOR, we are examining DOM dynamics in two contrasting Delaware coastal systems, the Murderkill River and Indian River Bay. This work employs fluorescence spectroscopy, Fourier transform ion cyclotron resonance mass spectrometry, and dissolved organic carbon and nutrient quantifications to better understand how hydrological factors (e.g., rainfall), watershed pressures (e.g., agriculture, development), and natural biological processes influence DOM quantities and composition in these two systems.

Surfactant Organics at the Air-Sea Interface The sea surface microlayer is the tens of microns thick layer separating the ocean from the atmosphere. This thin skin on the surface of the ocean has distinct biological, physical, and chemical characteristics that influence the exchange of particles and gases between the ocean and atmosphere. Surfactant compounds that accumulate at the microlayer have specific chemical structures that decrease the surface tension of the microlayer thereby limiting the exchange of biologically (e.g., oxygen, carbon dioxide) and climate (e.g., carbon dioxide, methane, nitrous oxide, dimethyl sulfide) relevant gases. The oceanographic conditions that influence the accumulation of these surfactants are, however, not well described. With this NSF project we are collaborating with Dr. Amanda Frossard’s group at the University of Georgia to explore the links between oceanography, light, biology, molecular level surfactant composition, and surface tension to provide a better understanding of these dynamics.

Biogeochemical Impacts of Prescribed Burns on Salt Marsh systems In coastal salt marsh systems, wrack and vegetation are burned by coastal managers to reduce the chances of wildfires that would otherwise threaten coastal communities and/or to remove invasive species such as Phragmites australis and restore native vegetation. These fires also introduce unburned biomass remains, or biochar, to the environment. Biochars, due to their unique physicochemical properties, may actually provide additional ecosystem services to salt marshes by 1) increased nitrogen and phosphorus removal and 2) increased carbon storage. If so, these prescribed burns may improve downstream water quality and removing carbon from the climate system. With this work, funded by the NOAA National Estuarine Research Reserve (NERR) Science Collaborative, we are collaborating with the Delaware NERR to explore the biogeochemical impacts of prescribed burns in salt marsh ecosystems. As a result of this work, we will provide a clearer picture of the value of prescribed burns enabling end user partners throughout Delaware to better assess their utility in lands that they manage.

Sulfurization and Carbon Accumulation in Salt Marshes Salt marshes are highly productive, coastal ecosystems providing numerous natural and economic ecosystem services including nutrient and pollutant filtration, providing bird, fish, and shellfish habitat, and sequestering carbon in its soils. In fact, salt marshes sequester this ‘blue carbon’ at rates that far exceed that of terrestrial forests, for example, making it a potential coal precursor. Just which mechanisms lead to these very high carbon accumulation and sequestration rates is not exactly clear, but a process called sulfurization may be an important contributor. With funding from the American Chemical Society Petroleum Research Fund, we are examining sulfurization in the Great Marsh in Lewes, DE to understand its relative importance to carbon accumulation in these systems as well as exploring the molecular level characteristics of sulfurized organic matter. Our work will help understand carbon cycling in salt marshes and the molecular level details of this globally important process.

Dissolved Organic Matter at Hydrothermal Vents

Oceanic dissolved organic carbon (DOC) is one of the largest reservoirs of reduced carbon on Earth. Most of this DOC is housed in the deep ocean, where it cycles extremely slowly. Radiocarbon dating shows that the oldest components of oceanic DOC are condensed aromatic compounds. These compounds are also presumed to be unreactive and persistent. This project will investigate whether mid-ocean ridge hydrothermal vents are a source for this fraction of deep ocean DOC, through a field campaign in Spring 2025 at the well-studied East Pacific Rise 9°N hydrothermal site. Results of this work will advance the understanding of slowly cycling aromatic carbon pools in the abyssal ocean and its sediments, which controls the sequestration of carbon on short and geologic timescales. Stay tuned!